Foam-in-place packaging is a known technique for producing cushioning packaging for fragile articles to be shipped. Foam-in-place packaging comprises generating foam cushioning on an as-needed basis while the article to be protected is being packaged. In general, foam-in-place packaging employs foamable compositions that are produced by bringing together two or more precursor chemicals that react and form foam when mixed together. The chemicals are generally selected from among those chemicals that when mixed form polymeric foams that harden upon curing. For example, a liquid polyol-containing precursor and a liquid isocyanate-containing precursor may be mixed and reacted to form a polyurethane foam. The resulting foam occupies a volume that is many times the volume of the liquid precursors.
One technique for foam-in-place packaging is to place the article to be packaged in a container, and then to place one or more flexible plastic bags containing a foamable composition into the container. The foamable composition expands to cause the bag to fill the void space between the walls of the container and the article, and then hardens. The result is a foam cushion that conforms closely to the shape of the article and the container, and thereby cushions and protects the article. This technique is referred to herein as the foam-in-bag technique.
A number of automated devices have been developed for rapidly making a relatively large number of bags for foam-in-bag packaging, and are assigned to the assignee of the present application. Exemplary devices are described and claimed in U.S. Pat. Nos. 4,674,268; 4,800,708; 4,854,109; and 5,376,219. Because these devices mix the precursors together as they are placed in the bags, the resulting bags must be placed in the containers with the articles immediately. Accordingly, these devices are particularly suitable for use in situations where it is desirable and feasible to make the bags containing the foam precursors at the location where articles are being packaged.
However, in certain applications, it may not be desirable to employ such automated devices to make foam-in-bag packaging directly at the packaging location. Accordingly, an article for foam-in-bag packaging use has been developed in which the precursor chemicals are contained in a bag and kept separated from one another until it is desired to form a foam cushion. At that time, the bag may be manipulated to cause breakage of a frangible membrane that separates the two precursors and to mix the precursors together. The bag is then placed into the packaging container adjacent the article to be protected. The precursors react to form foam, and the bag expands to fill the void space and cures to form a cushion. Commonly owned U.S. Pat. Nos. 5,699,902; 5,899,326; 5,996,782; and 6,272,813 describe various bags of this type and systems for their production.
The speed of the foam-forming reaction and the final volume of the expanded foam generally depend on the temperature of the precursors; both the reaction speed and final volume tend to increase with increasing precursor temperature. Accordingly, heating devices for heating foam-in-bag packaging bags prior to use have been developed, as described in commonly owned U.S. Pat. Nos. 5,986,239 and 6,065,636. Heating the bags to a consistent temperature tends to result in the cushions having a predictable final volume, thereby improving the consistency and quality of the overall packaging operation. The heaters described in the '239 and '636 patents are designed to house a plurality of foam-in-bag packaging bags that are each folded into a compact arrangement and held in the folded condition by a band that encircles the folded bag. The folded bags are loaded into the heater and held there for a period of time until they are needed. Desirably each bag is held in the heater long enough to reach a desired elevated temperature, such as about 120° F., prior to being removed from the heater for use. In a busy packaging line where bags are continually being removed from the heater and replaced with unheated bags, it is possible to lose track of how long each bag has been in the heater, and hence a bag may be removed from the heater and used before the bag has reached the desired temperature. The heater described in the '636 patent includes a loading and dispensing arrangement for the bags that tends to ensure that the bags are used on a first-in, first-out basis, but it is possible to circumvent this arrangement. Additionally, the heater of the '636 patent relies on convective heating to warm the bags, which tends to be less efficient than the conductive heating employed in the '239 patent.
The heaters of the '239 and '636 patents also necessitate that the bags each be individually folded and banded. The production of such bags thus requires steps of separating bags from the continuous web of bags that comes off a manufacturing machine, folding each individual bag, and applying a band or the like to hold the bag in its folded configuration. To use a bag, the band must be removed and the bag must be unfolded.